Final answer:
Foaming in a boiler is primarily caused by high concentrations of solids in the water, which can lead to the formation of foam and scale when combined with calcium and carbonate ions.
Step-by-step explanation:
The main answer to the question of what causes foaming in a boiler is solids too high in concentration. Foaming can be exacerbated by several factors such as high levels of dissolved solids, rapid boiling, or reactions in the water. A common contributory factor to foaming is the presence of hard water, which contains excess calcium and magnesium ions that can react with bicarbonate ions, leading to the formation of calcium carbonate precipitates, and resultant foaming and scaling within the boiler. When the water is heated, carbon dioxide that was previously dissolved can escape into the gas phase, which can cause these precipitates to work their way to the surface and form a layer of foam. Additionally, improper water treatment like inadequate coagulation, and flocculation can fail to remove dissolved particles, exacerbating the issue. In conclusion, to prevent or mitigate boiler foaming, it is essential to manage the chemistry of the feed water effectively, including monitoring and controlling the levels of dissolved and suspended solids.